In general, armrests provided at seats of vehicles could be put in a vertical posture when they are not used and the armrests could be rotated to a horizontal posture when they are used, thereby maximizing the use of available space. In such a rotatable armrest, a rotation axis is fixed to a seat back, other constituent parts such as a recliner, etc. are also fitted to the seat back, and it is not desirable that a front end of the armrest when vertical protrudes from the top end of the seat back. Accordingly, the length of the armrest is restricted.
However, for the purpose of convenient use of the armrest, the arm rest must have a maximum length. Specifically, when a cup holder, etc. is provided at the front end of the armrest, the armrest should be long enough to allow a user to use the cup holder with a comfortable posture. Accordingly, it would be desirable to provide an armrest that addresses the above drawbacks and requirements.